Most engines of trucks commonly used in the trucking industry now utilize fuel injectors to deliver and atomize fuel charge to the engine cylinders. An electronic timing circuit delivers precisely timed electrical pulses for operation of the fuel injector. Such pulses are used in a solenoid stator assembly to reciprocate a solenoid poppet and armature assembly mounted in the fuel injector valve which controls the injection of fuel into the associated engine cylinder.
The solenoid stator assembly commonly requires a housing to protect its electrical components and to locate them precisely in relation to the reciprocating solenoid poppet and armature assembly. Commonly, such housings have involved insulative plastic housing components surrounding a stator core. The stator core extends through a stator coil which is pulsed with the electrical current to generate the magnetic forces necessary to reciprocate the poppet and armature assembly. In the design of such stator assemblies, it is necessary to overcome severe difficulties created by the very harsh working environment in which the assembly must function.
The stator assembly must be able to accommodate wide variations in operating temperature from cold startup at below zero temperatures to under the hood temperatures in hot desert conditions, causing significant thermal expansion and contraction of the housing components. High internal cavity valve pressure from within the injector valve can create high pressure within the interior of the plastic housing leading to cracking of the plastic. Over time and under these conditions of vibration and fluctuating temperature, plastic components of a housing can develop cracks and hairline fractures. Moreover, the plastic housing components can eventually become embrittled. Also, plastic components are at risk of impact damage if persons servicing the engine accidentally impact them with wrenches or other tools during the course of working on adjacent structures. Fuel injectors under current conditions of operations operate at fuel injection pressures on the order of 2,000 pounds per square inch pressure. Fuel under such high working pressures from mechanical portions of the fuel injector valve can direct extremely high pressure of fuel against the plastic stator housing mounting surface. The entry of such fuel between the stator and the insulative plastic housing tends to expand and increase the area and can cause eventual failure of the housing.
Various types of solenoid stator assemblies have been developed to address the aforementioned problems. One such stator assembly is shown in U.S. Pat. No. 5,155,461 to Teerman et al. For "solenoid stator assembly for electronically actuated fuel injectors and method of manufacturing same", owned by Diesel Technology Corporation. The Teerman patent discloses an actuator assembly for use with a fuel injector, the actuator assembly having an E-shaped stator core having outer and central pole pieces received within a plastic housing that is bolted to a mounting base on the fuel injector. To prevent passage of leaking fuel under high pressure between the stator core and the housing, the Teerman device incorporates T-shaped notches in the outer faces of the stator pole pieces into which the plastic material of the housing is molded to present a barrier against the passage of fuel. The Teerman device is constructed by a process which involves prestressing the outer pole pieces of the core outwardly before the housing is molded about it. The prestressing provides restorative forces to oppose additional, fuel pressure related forces that might be applied to the outer pole pieces and inhibit additional displacement.
While the T-shaped slots in the outer pole pieces of the Teerman may be effective to resist fuel migration, it may require an additional machining step to provide such T-shaped slots thereby contributing to the manufacturing cost of the stator core. In addition, the need to prestress the outer pole pieces before molding the housing around the stator core requires additional process steps during the manufacturing process.
The present invention is directed to overcoming one or more of the problems set forth above.